(Business 2.0) – AT&T already sold off its cable and wireless assets; now the telecom giant is moving beyond its circuit-switched telephone infrastructure. Having paved the way with billions of dollars' worth of data-network upgrades over the last few years, the company will test voice-over-Internet-protocol (VOIP) phone service in several cities during early April, with plans to expand into 100 markets by year's end. Switching to VOIP makes obvious sense; however, in the short run, it may cannibalize AT&T's circuit-switched cash cow. But when it comes to cannibalizing, better to do it yourself than to wait for others to eat your lunch.